Freelance Traveller

Collapsible Fuel Tanks and Jump Drives “On Rails”

by Joshua Levy

This article describes two new fittings for starships. The examples are provided using Classic Traveller and Cepheus Engine rules, but the fittings can be used with any Traveller ruleset.

Collapsible Fuel Tanks

Though the name has been used before for a variety of alternative fuel-carriage mechanisms, this version of collapsible fuel tanks are a spaceship fitting generally used by ships that need more maneuver fuel than jump fuel. Ships which need extra jump fuel generally use external drop tanks or internal temporary fuel bladders, which are described elsewhere.

The collapsible fuel tanks described here permanently use 10% of the tank size (minimum 5 tons) to store the tank itself, when empty. Even when in use, this space is not part of the tank. When in use, or “deployed”, the tank expands to its full size to store fuel, making the ship that much larger. The tank can be used over and over. Deployment and takedown are automated and can be controlled from the ship’s bridge. The process is not quick, taking about 1 minute per 100 tons of tank size, with a minimum of 4 minutes. The tank must be empty, and any tiny scraps of fuel left in the tank will be vented to space. Finally, the ship cannot jump with the collapsible fuel tank in use; the temporary hull around it is not jump capable. Referees should decide if the jump drives just won’t engage or if a misjump results.

Collapsible Fuel Tanks can be included at build time at a cost of Cr10,000 per ton of fuel capacity. Retrofitting Collapsible Fuel Tanks to an already-built ship costs 10% of the original hull construction cost, plus Cr10,000 per ton of fuel capacity.

Consider, for example, the Classic Traveller Type S Scout modified with an 8-ton collapsible tank (perhaps by removing two staterooms). When deployed, the tank can hold 80 tons of fuel. It takes 4 minutes to deploy or take down the tank. If the ship is sent to explore a large system, with only one fuel source, it will jump in system with the fuel tank collapsed, but can fill up after arrival. It now has a total fuel capacity of 120 tons, but a total size of 180 tons. Therefore, it has 1G acceleration, but a range of 6 months, rather than the normal 2G, 1 month range. (The advantages are even larger for a 400 ton exploratory ship with a 100 or 200 ton collapsible fuel tank.)

A Cepheus Engine TL9 Courier would end up with a fuel capacity of 108 tons (giving it an in-system endurance of 54 weeks). The design would probably sacrifice 8 tons of cargo space, rather than 2 staterooms.

Jump Drives “On Rails”

When a spaceship operates in only one system, but needs to be built in a different system, it may be built with jump drives “on rails”. The formal name is “Jump Drives Removable on Arrival”. These ships are built with room for Jump drives, however instead of new jump drives, used drives are installed, and the general design of the ship allows for relatively easy removal in zero-G. Usually a modular replacement for the jump drive is also constructed. When the ship is delivered to its final destination, the jump drives are removed and the modular replacements installed. The swap takes a week or two, depending on the situation. The referee may roll 2- for a catastrophic failure of some kind. (This roll, and the reverse roll discussed later, both assume that the people doing the swap have Engineering skill, and at least half the people involved have done it before. If they don’t have the experience, apply DM -2; if they lack both skill and experience, DM -8.) Jump drives “on rails” end up wasting 3% (minimum 1 ton) of the jump drive space in the engineering section. So a B Jump drive installed “on rails” would take up 16 tons of space, but when replaced, gives back 15 tons of space.

Because the jump drive is in the engineering area of the ship, whatever replaces it will also be there. Some stellar governments may ban this, as it is dangerous. Others may allow it, but limit what is put in engineering in ways they think are safe, or require a post-conversion inspection. Obviously, if fuel is safe, then replacing the jump drive with fuel is straight forward. Cargo space or a small craft hanger may be good choices, if there is a reasonable way to get the cargo or craft in and out of engineering. This space cannot be used to upgrade to a larger power plant or maneuver drive, as that is a replacement, not adding new equipment.

Putting in staterooms (especially for engineers) might sound like a good idea to someone who does not spend time in space, but it’s not. Engineering spaces are usually bad places to work, and terrible places to live. There is often extreme noise, smells, vibrations, and hazardous materials. If people are living in engineering, it might be a good application of the Sanity Rules (published as “A Sanity System for Marc Miller’s Traveller (T4)”, Freelance Traveller, March/April 2016). Indeed, a whole horror themed adventure could be built around the engineering crew’s gradual loss of sanity. Maybe there will be rats in the walls…

A ship built with a jump drive “on rails” will be subject to two types of malfunctions that other ships are not subject to:

First, there could be a failure of the hull in engineering which was previously removed to replace the drive. This section could fail catastrophically, or could spring a leak, or generally show signs of imminent failure. Since it’s likely to be large, and will certainly be in engineering, any problem is likely to get the crew’s attention quickly (if it does not kill them outright).

Second, there could be a problem in the linkage between whatever replaced the jump drive, and the rest of the ship. These sections could lose power, life support/comfort conditioning, or networking connections, or they may start physically sliding around or vibrating.

If a spare jump drive is available, the swapping process can be reversed later, but this is unusual, and much more difficult than the initial swap. It will take the same one to two weeks, but the referee should roll 2d6 with a failure occurring on 3-, or even 4- for particularly old starships.

The delivery process for these ships typically works as follows. When the ship is ready, the buyer sends a pilot and engineer (and possibly more crew) to the shipyard. The shipyard provides some crew, and a cargo ship. The two vessels travel to the destination system. The buyer uses this as a shakedown or acceptance flight. Once at the final destination, the shipyard crew removes the jump drive and loads it back in their cargo ship, and then loads in whatever is replacing the jump drive. The buyer crew does the final shakedown/acceptance flights, and the spaceship is delivered.

This assumes a fair amount of trust between the shipyard and the buyer. If such trust is lacking, things can get more complex. The shipyard may provide the transport crew. The buyer may insist that the cargo ship stay at the destination system while the shakedown cruise is made. Since there are many millions of credits involved, things could get tense.

When the ship is designed with Jump Drive “on rails”, the additional cost is 0.1% of the hull cost, times the displacement of the drive to be so mounted. The drive itself costs “book” price.

It is unlikely that a Classic Traveller Type-S or a Cepheus Engine TL9 Courier would be built this way, but if either were, upon arrival at its final destination, its 15 ton Jump-B drive would be removed, giving the ship 14 extra tons of space. (Probably for cargo, but possibly for a small craft hanger, fuel, or even to carve out more staterooms.)

The author thanks Darrel Strom and John Redden for reviewing a draft of this article. All mistakes are my own.